1. Field of the Invention
This invention relates to a recombinant construct for providing a plant with resistance against a DNA virus and a RNA virus and a method thereof through the siRNA-mediated pathway, and the recombinant construct cannot be expressed as a protein product in plant.
2. Description of the Related Art
Global threats of crop diseases caused by virus have led to tremendous economic losses. For example, the ssDNA geminiviruses, which infect covering monocotyledons and dicotyledons, cause the crop diseases such as beet curly top, cassava mosaic, cotton leaf curl, maize streak and tomato leaf curl. The ssRNA tospovirus, which can infect a wide range of hosts, have been documented infecting over nine hundred different plant species from 82 different families.
The different genetic structures and molecular mechanisms of geminiviruses and tospoviruses necessitate applications of transcriptional gene silencing (TGS) and post-transcriptional gene silencing (PTGS), respectively, for their control. Both TGS and PTGS depend on small interfering RNAs (siRNA) or microRNAs (miRNA) that are produced from double-stranded RNA (dsRNA) precursors. TGS occurs in nuclei via RNA-directed DNA methylation (RdDM) at CG, CHG and CHH sequence contexts (where H=A, T or G), whereas PTGS operates in the cytoplasm through mRNA cleavage or inhibition of translation.
PTGS-mediated transgenic resistance has been well applied for the control of plant RNA viruses, including tospoviruses, however, in the case of ssDNA geminiviruses, most attempts using PTGS approach have only resulted in short delay in symptom development or reduced disease severity.
On the other hand, the transgenic plants may carry a marker gene such as antibiotic resistant genes or herbicide resistant genes or the like. However, the marker gene may be expressed as proteins in plant, and such approach may cause potential risks to ecology and is also concerns for food safety.
Therefore, it is a primary issue to provide a plant that has resistances against DNA virus and RNA virus both, and the foreign gene may not be expressed as a foreign protein in plant.